Hamilton Group
Encyclopedia
The Devonian
Hamilton Group is a mapped bedrock
unit in New York
, Pennsylvania
, Maryland
, and West Virginia
. In Virginia
, it is known as the laterally equivalent Millboro Shale.
The group is named for the village of Hamilton, New York
.
These rocks are the oldest strata
of the Devonian gas shale sequence.
, a dark gray, gray, brown, and olive laminated shale, siltstone, and very fine-grained sandstone or claystone containing marine fossils, overlying the Marcellus Shale, a fissile
gray-black to black, thinly laminated, pyritic
, carbonaceous
thin shale with sparse marine fauna and siderite concretions. The total thickness of the Hamilton Group in Pennsylvania runs approximately 970 feet. In New York State, it thickens from 250 feet near Lake Erie
to over 2,500 feet in Ulster and Greene
counties, with depths ranging from outcrops to 8,000 feet below the surface of Sullivan County
, in the southeastern part of the state.
In the interior lowlands of New York, the Hamilton Group contains the Marcellus, Skaneateles, Ludlowville, and Moscow Formations, in ascending order, with the Tully Limestone above. These units are divided by the Stafford, Centerfield, and Tichenor limestones. In Ontario
, Canada, the Hamilton Group formations are, in ascending order, Bell, Rockport Quarry, Arkona, Hungry Hollow, Widder and Ipperwash; the Kettle Point Formation lies unconformably above.
The Mahantango Formation includes the following members, in descending order: Tully argillaceous limestone, Sherman Ridge, Montebello sandstone, Fisher Ridge, Dalmatia, and Turkey Ridge. In south-central Pennsylvania, it includes Clearville, Frame, Chaneysville, and Gander Run Members. Its thickness in Maryland ranges from 600 feet in the west, increasing to 1,200 feet in the east, and approximately 1000 feet thick in central Pennsylvania.
The Marcellus Formation contains a local limestone Purcell Member and Tioga bentonite at the base in eastern Pennsylvania. Its thickness in Maryland ranges from 250 feet in east, increasing to 500 feet in the west, but is only approximately 70 feet thick in central Pennsylvania.
The Hamilton Group, Tioga Metabentonite Bed, and Needmore Shale formerly were designated as the Romney Formation.
period. In Maryland, it rests conformably atop the Tioga Metabentonite Bed of thinly laminated shale with a thickness less than one foot over the Needmore Shale, and conformably below the Brallier Formation
(formerly Woodmont Shale) dark laminated shale in the east, Harrell Shale dark laminated shale in the west, and Tully Limestone in the subsurface of Garrett County. In Pennsylvania it lies atop the Onondaga Formation limestone and shale forming a sharp conformable contact with the Selinsgrove Limestone of that formation, and lies beneath the Portage (Brallier, Harrel, Burkett) dark shales of the Harrell Formation
.
and building stone, that is used locally for shale aggregate and common fill.
Devonian
The Devonian is a geologic period and system of the Paleozoic Era spanning from the end of the Silurian Period, about 416.0 ± 2.8 Mya , to the beginning of the Carboniferous Period, about 359.2 ± 2.5 Mya...
Hamilton Group is a mapped bedrock
Bedrock
In stratigraphy, bedrock is the native consolidated rock underlying the surface of a terrestrial planet, usually the Earth. Above the bedrock is usually an area of broken and weathered unconsolidated rock in the basal subsoil...
unit in New York
New York
New York is a state in the Northeastern region of the United States. It is the nation's third most populous state. New York is bordered by New Jersey and Pennsylvania to the south, and by Connecticut, Massachusetts and Vermont to the east...
, Pennsylvania
Pennsylvania
The Commonwealth of Pennsylvania is a U.S. state that is located in the Northeastern and Mid-Atlantic regions of the United States. The state borders Delaware and Maryland to the south, West Virginia to the southwest, Ohio to the west, New York and Ontario, Canada, to the north, and New Jersey to...
, Maryland
Maryland
Maryland is a U.S. state located in the Mid Atlantic region of the United States, bordering Virginia, West Virginia, and the District of Columbia to its south and west; Pennsylvania to its north; and Delaware to its east...
, and West Virginia
West Virginia
West Virginia is a state in the Appalachian and Southeastern regions of the United States, bordered by Virginia to the southeast, Kentucky to the southwest, Ohio to the northwest, Pennsylvania to the northeast and Maryland to the east...
. In Virginia
Virginia
The Commonwealth of Virginia , is a U.S. state on the Atlantic Coast of the Southern United States. Virginia is nicknamed the "Old Dominion" and sometimes the "Mother of Presidents" after the eight U.S. presidents born there...
, it is known as the laterally equivalent Millboro Shale.
The group is named for the village of Hamilton, New York
Hamilton (village), New York
The Village of Hamilton is a village located within the town of Hamilton in Madison County, New York, USA.-Geography and climate:The village, located at , lies in the Chenango Valley, just south of the headwaters of the Chenango River. The village is approximately southeast of Syracuse and ...
.
These rocks are the oldest strata
Stratum
In geology and related fields, a stratum is a layer of sedimentary rock or soil with internally consistent characteristics that distinguish it from other layers...
of the Devonian gas shale sequence.
Description
The Hamilton Group consists of the Mahantango FormationMahantango Formation
The Devonian Mahantango Formation is a mapped bedrock "unit" in Pennsylvania, New Jersey, New York and Maryland. It is named for the North branch of the Mahantango Creek in Perry and Juniata counties in Pennsylvania. It is a member of the Hamilton Group, along with the underlying the Marcellus...
, a dark gray, gray, brown, and olive laminated shale, siltstone, and very fine-grained sandstone or claystone containing marine fossils, overlying the Marcellus Shale, a fissile
Fissility (geology)
Fissility refers to the property of rocks to split along planes of weakness into thin sheets. This is commonly observed in shales, which are sedimentary rocks, and in slates and phyllites, which are foliated metamorphic rocks. The fissility in these rocks is caused by the preferred alignment of...
gray-black to black, thinly laminated, pyritic
Pyrite
The mineral pyrite, or iron pyrite, is an iron sulfide with the formula FeS2. This mineral's metallic luster and pale-to-normal, brass-yellow hue have earned it the nickname fool's gold because of its resemblance to gold...
, carbonaceous
Carbonaceous
Carbonaceous is the defining attribute of a substance rich in carbon. Particularly, carbonaceous hydrocarbons are very unsaturated, high-molecular-weight hydrocarbons, having an elevated carbon:hydrogen ratio....
thin shale with sparse marine fauna and siderite concretions. The total thickness of the Hamilton Group in Pennsylvania runs approximately 970 feet. In New York State, it thickens from 250 feet near Lake Erie
Lake Erie
Lake Erie is the fourth largest lake of the five Great Lakes in North America, and the tenth largest globally. It is the southernmost, shallowest, and smallest by volume of the Great Lakes and therefore also has the shortest average water residence time. It is bounded on the north by the...
to over 2,500 feet in Ulster and Greene
Greene County, New York
Greene County is a county located in the U.S. state of New York. Its name is in honor of the American Revolutionary War general Nathanael Greene. Its county seat is Catskill...
counties, with depths ranging from outcrops to 8,000 feet below the surface of Sullivan County
Sullivan County, New York
Sullivan County is a county located in the U.S. state of New York. As of the 2010 census, the population was 77,547. The county seat is Monticello. The name is in honor of Major General John Sullivan, who was a hero in the American Revolutionary War...
, in the southeastern part of the state.
In the interior lowlands of New York, the Hamilton Group contains the Marcellus, Skaneateles, Ludlowville, and Moscow Formations, in ascending order, with the Tully Limestone above. These units are divided by the Stafford, Centerfield, and Tichenor limestones. In Ontario
Ontario
Ontario is a province of Canada, located in east-central Canada. It is Canada's most populous province and second largest in total area. It is home to the nation's most populous city, Toronto, and the nation's capital, Ottawa....
, Canada, the Hamilton Group formations are, in ascending order, Bell, Rockport Quarry, Arkona, Hungry Hollow, Widder and Ipperwash; the Kettle Point Formation lies unconformably above.
The Mahantango Formation includes the following members, in descending order: Tully argillaceous limestone, Sherman Ridge, Montebello sandstone, Fisher Ridge, Dalmatia, and Turkey Ridge. In south-central Pennsylvania, it includes Clearville, Frame, Chaneysville, and Gander Run Members. Its thickness in Maryland ranges from 600 feet in the west, increasing to 1,200 feet in the east, and approximately 1000 feet thick in central Pennsylvania.
The Marcellus Formation contains a local limestone Purcell Member and Tioga bentonite at the base in eastern Pennsylvania. Its thickness in Maryland ranges from 250 feet in east, increasing to 500 feet in the west, but is only approximately 70 feet thick in central Pennsylvania.
The Hamilton Group, Tioga Metabentonite Bed, and Needmore Shale formerly were designated as the Romney Formation.
Subunits
- The Geneseo Shale is a dark grey to black shale that overlies the Tully Limestone; it includes the Filmore beds.
- The Tully Limestone is a shallow-water carbonaceous unit.
- The Moscow Formation (Middle Devonian / Givetian) comprises grey to black shales interbedded with limestones and calcareous mudstones and usually bioturbated.
Distribution
The distribution of the unit can be observed on this map.
Age
Relative age dating of the Hamilton places it in the middle and lower DevonianDevonian
The Devonian is a geologic period and system of the Paleozoic Era spanning from the end of the Silurian Period, about 416.0 ± 2.8 Mya , to the beginning of the Carboniferous Period, about 359.2 ± 2.5 Mya...
period. In Maryland, it rests conformably atop the Tioga Metabentonite Bed of thinly laminated shale with a thickness less than one foot over the Needmore Shale, and conformably below the Brallier Formation
Brallier Formation
The Devonian Brallier Formation is a mapped bedrock unit in Pennsylvania, Maryland, West Virginia, and Virginia.-Description:The Brallier Formation was described by Charles Butts in 1918 as a fine-grained, siliceous shale with few fine-grained sandstone layers, from outcrops in central Pennsylvania...
(formerly Woodmont Shale) dark laminated shale in the east, Harrell Shale dark laminated shale in the west, and Tully Limestone in the subsurface of Garrett County. In Pennsylvania it lies atop the Onondaga Formation limestone and shale forming a sharp conformable contact with the Selinsgrove Limestone of that formation, and lies beneath the Portage (Brallier, Harrel, Burkett) dark shales of the Harrell Formation
Harrell Formation
The Devonian Harrell Formation is a mapped bedrock unit in Pennsylvania, Maryland, West Virginia, and Virginia.-Description:The Harrell Formation was first described by Charles Butts in 1918...
.
Economic uses
The Hamilton is a good source of road material, riprapRiprap
Riprap — also known as rip rap, rubble, shot rock or rock armour or "Rip-rap" — is rock or other material used to armor shorelines, streambeds, bridge abutments, pilings and other shoreline structures against scour, water or ice erosion.It is made from a variety of rock types, commonly granite or...
and building stone, that is used locally for shale aggregate and common fill.
See also
- Geology of PennsylvaniaGeology of PennsylvaniaThe Geology of Pennsylvania consists of six distinct physiographic provinces, three of which are subdivided into different sections. Each province has its own economic advantages and geologic hazards and play an important role in shaping everyday life in the state...